Kinesin is a mechanoenzyme that drives microtubule-based intracellular organelle transport processes. Kinesin couples a free-energy-liberating chemical reaction (the hydrolysis of ATP) to a cycle of mechanical processes that move the enzyme molecules and attached organelles along microtubules. We want to characterize the cycle of mechanical processes by which kinesin moves and to determine how these processes are coupled to the reactions of ATP hydrolysis. We have developed novel experimental systems that allow us to directly monitor nanometer-scale mechanical processes, domain movements, and chemical steps in single isolated kinesin molecules using light microscope-based instruments. Intracellular organelle transport by kinesin and kinesin homologs plays an essential role in the physiology of eukaryotic cells. Its functions include transport of materials, chromosome and nuclear movements in mitosis/meiosis, and morphogenesis of membranous organelles. To explore these functions at the molecular level we will: Characterize the conformational changes in the kinsin alpha-helical coiled-coil neck domain that are required for processive motility along microtubules. Test the hand-over-hand hypothesis for the kinesin movement mechanism Detect and characterize the power stroke of an isolated kinesin head domain. The experiments will combine single-molecule biophysics techniques with conventional enzymology methods including protein chemical modification, site-directed mutagenesis, and chemical kinetics techniques.